1. Field of the Invention
This invention relates to phosphors for color televisions. More particularly, the invention relates to phosphors for color televisions which phosphors are surface-treated for improving the light-exposure sensitivity of phosphor slurries prepared therefrom for formation of phosphor screens.
2. Description of the Prior Art
As is well known, phosphor screens for color television cathode ray (picture) tubes are composed of blue, green, and red emitting phosphor dots or stripes of blue, green, and red emitting phosphor components disposed regularly on a face plate. The phosphor screens for color television picture tubes are prepared by a photoprinting method. That is, a first light emitting phosphor component is dispersed in a solution of a light sensitive resin such as, for example, an aqueous solution of polyvinyl alcohol activated with a dichromate, to provide a phosphor slurry. The phosphor slurry obtained is applied over the whole surface of a face plate by an appropriate coating method such as by rotary coating, etc. (slurry coating), and then the coated layer is irradiated by energy rays or actinic rays such as ultraviolet rays, etc., in conformity with a desired pattern, whereby the resin is hardened and insolubilized at the portions irradiated by the energy rays (light exposure). Thereafter, the resin at the non-irradiated portions (unhardened resin portions) is dissolved away by a solvent, etc. (development) to form dots or stripes composed of the first light emitting phosphor component. Then, by successively repeating slurry coating, exposure and development in the same manner as described above using second and third light emitting phosphor components, dots or stripes composed of the second and third light emitting phosphor components are formed on the face plate. In this case, as a matter of course, the energy ray irradiation must be so controlled that the dots or stripes composed of each of the first, second, and third light emitting phosphor components are repeatedly and regularly disposed on the face plate without being overlapped with each other. Then, the fluorescent screen containing the resin component thus prepared is fired at a proper temperature to decompose and volatilize the resin component, whereby a desired phosphor screen is obtained.
For making phosphor screens for color television picture tubes by a photoprinting method using the above-mentioned phosphor slurries, the following requirements must be met.
1. The phosphor screen must have sufficient thickness and be composed of densely arranged minute dots or stripes of phosphor components;
2. The dots or stripes of phosphor components must be formed in the desired shape at desired positions on a face plate;
3. The light emitting phosphors must not intermix with each other, i.e., color mixing must not occur;
4. The light exposure sensitivity of phosphor slurries must be high and the phosphor slurries have to be easy to work with.
Hitherto, various investigations have been made on the compositions, preparation methods, etc., of phosphor slurries as well as the surface treatment of phosphors (blue, green and red emitting phosphor components) for color television with the aim of satisfying the above-mentioned requirements and the presently used phosphor slurries do in fact satisfy these requirements to some extent. However, from a commercial viewpoint phosphor screens having even higher quality are constantly sought after and hence it has been desired to meet the above requirements more completely.